JPH0791297A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To enable a high precision air-fuel ratio control by resolving the problem of response delay of an air-fuel ratio sensor arranged on an exhaust pipe downstream from a catalytic converter. CONSTITUTION:The furture value of a downstream air-fuel ratio sensor after the delay time passes is estimated by the hysteresis of the output of the past fixed period of an upstream air-fuel ratio sensor 13 arranged in an exhaust passage upstream from a catalytic converter 12 and the present output of the downstream air-fuel ratio sensor 15 arranged in the exhaust passage downstream from the catalytic converter, and also the output of the upstream air-fuel ratio sensor 13 is corrected on the basis of this estimated output, so as to perform the air-fuel ratio feedback control. Thereby, the response delay of the downstream air-fuel ratio sensor can be substantially made zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly, to a combustion air-fuel ratio of an engine based on the outputs of air-fuel ratio sensors arranged upstream and downstream of an exhaust purification catalytic converter. The present invention relates to an air-fuel ratio control device for an internal combustion engine that controls the engine.

[0002]

2. Description of the Related Art There is known a technique in which a three-way catalytic converter is arranged in an exhaust passage of an internal combustion engine to purify three harmful components of NO _x , HC and CO in the exhaust gas at the same time. Further, the three-way catalyst can purify the above three components simultaneously only when the air-fuel ratio of the inflowing exhaust gas is in an extremely narrow range near the stoichiometric air-fuel ratio. Maintaining the vicinity is important for maintaining good exhaust properties. For this purpose, an air-fuel ratio sensor such as an O ₂ sensor is provided on the upstream side of the catalytic converter in the exhaust passage to detect the exhaust air-fuel ratio actually flowing into the catalytic converter, and the exhaust air-fuel ratio is adjusted based on the detected exhaust air-fuel ratio. Feedback control of the fuel supply amount to the engine is generally performed so as to maintain the stoichiometric air-fuel ratio. (In this specification, the ratio of the amount of air and the amount of fuel supplied to the exhaust passage on the upstream side of the catalytic converter, the engine combustion chamber, the intake passage, etc. is called the exhaust air-fuel ratio, and The air-fuel ratio of combustion is referred to as the combustion air-fuel ratio, and therefore, when fuel or secondary air is not supplied to the exhaust passage upstream of the catalytic converter, the exhaust air-fuel ratio and the combustion air-fuel ratio match. However, when the engine combustion air-fuel ratio is controlled according to the output signal of the air-fuel ratio sensor provided on the upstream side of the catalytic converter as described above, a problem may actually occur.

That is, when the above-mentioned control is performed, variations in the output characteristics of the individual air-fuel ratio sensors are directly reflected in the control, so that the accuracy of the air-fuel ratio control may deteriorate. Further, the exhaust gas discharged from each cylinder is not uniformly mixed on the upstream side of the catalytic converter, and depending on the arrangement of the upstream side air-fuel ratio sensor, the sensor detects the exhaust air-fuel ratio fluctuation of a specific cylinder. As a whole, it may be difficult to accurately control the exhaust air-fuel ratio flowing into the catalytic converter to be close to the stoichiometric air-fuel ratio. Further, since the exhaust gas temperature is high on the upstream side of the catalytic converter and the air-fuel ratio sensor is easily deteriorated, the same problem occurs even when the sensor output characteristics change over time due to the deterioration.

To solve this problem, in addition to the upstream air-fuel ratio sensor, an air-fuel ratio sensor (downstream air-fuel ratio sensor) is also arranged in the exhaust passage on the downstream side of the catalytic converter, and the output of the upstream air-fuel ratio sensor is set. A so-called double sensor system has been proposed in which, in addition to signal-based air-fuel ratio control, air-fuel ratio control is performed based on the output of a downstream side air-fuel ratio sensor (see Japanese Patent Laid-Open No. 63-195351).

On the downstream side of the catalytic converter, since the exhaust gas from each cylinder is uniformly mixed, the downstream side air-fuel ratio sensor is less affected by the specific cylinder, and the exhaust gas temperature is lower than that on the upstream side. As a result, there is little change in output characteristics due to sensor deterioration. Therefore, in the double sensor system, by correcting the air-fuel ratio feedback control by the upstream air-fuel ratio sensor based on the output of the downstream air-fuel ratio sensor, the air-fuel ratio due to the secular change or variation in the output characteristics of the upstream air-fuel ratio sensor The control deviation is corrected by the downstream air-fuel ratio sensor, and more accurate air-fuel ratio control is performed.

[0006]

However, in the double sensor system, the downstream side air-fuel ratio sensor has a problem that the detection of the air-fuel ratio change is delayed as compared with the upstream side air-fuel ratio sensor due to the O ₂ storage action of the three-way catalyst. is there. Generally, a three-way catalyst adsorbs oxygen in the exhaust when the exhaust air-fuel ratio is larger than the theoretical air-fuel ratio (when the air-fuel ratio is lean), and when the exhaust air-fuel ratio is smaller than the theoretical air-fuel ratio (when the air-fuel ratio is rich). It has a so-called O ₂ storage function of releasing oxygen. Due to this O ₂ storage action, even if the exhaust air-fuel ratio flowing into the three-way catalytic converter deviates from the stoichiometric air-fuel ratio for a short time, the air-fuel ratio of the atmosphere of the three-way catalyst can be maintained near the stoichiometric air-fuel ratio. It is possible to maintain good exhaust purification performance of the catalyst, but on the other hand, changes in the exhaust air-fuel ratio on the downstream side of the catalytic converter due to the adsorption and release of oxygen by the three-way catalyst cause changes in the exhaust air-fuel ratio on the upstream side. It occurs later than the change.

For example, even when the exhaust air-fuel ratio on the inlet side of the catalytic converter changes from lean to rich near the stoichiometric air-fuel ratio, the exhaust air-fuel ratio on the outlet side of the catalytic converter releases oxygen stored in the three-way catalyst. It does not change immediately during the operation, but changes to the rich side after the oxygen stored in the three-way catalyst is exhausted, that is, after a certain time delay. Therefore, for some reason while controlling the air-fuel ratio near the stoichiometric air-fuel ratio, for example, when the exhaust air-fuel ratio starts to shift to the rich air-fuel ratio side, the downstream side air-fuel ratio sensor shifts to the rich side of the air-fuel ratio. At the time of detection, the exhaust air-fuel ratio on the upstream side has already largely shifted to the rich side, and it becomes difficult to control the exhaust air-fuel ratio accurately near the stoichiometric air-fuel ratio. Also, a similar time delay occurs when changing from the rich air-fuel ratio to the lean air-fuel ratio.

In the double sensor system of Japanese Patent Laid-Open No. 63-195351 mentioned above, in order to solve the problem of time delay in detecting the air-fuel ratio change of the downstream side air-fuel ratio sensor, the air detected by the downstream side air-fuel ratio sensor is solved. The larger the deviation between the fuel ratio and the stoichiometric air-fuel ratio, the larger the update amount of the control constant of the feedback control by the upstream air-fuel ratio sensor per unit time is to shorten the time for the air-fuel ratio to converge to the stoichiometric air-fuel ratio. . However, in the double sensor system of the publication, since the update amount of the control constant is determined using the output of the current downstream side air-fuel ratio sensor which is still detected with a certain time delay, for example, the downstream side air If the outputs of the fuel ratio sensors are the same, the update amount will be determined regardless of whether the upstream air-fuel ratio is shifting to the rich side or the lean side. Therefore, in the double sensor system of the above publication, there is a problem that the responsive air-fuel ratio control reflecting the air-fuel ratio change tendency is not always performed.

In view of the above problems, the present invention solves the problems caused by the time delay of the output of the downstream side air-fuel ratio sensor,
An object of the present invention is to provide an air-fuel ratio control device that improves control response and enables highly accurate air-fuel ratio control.

[0010]

According to the present invention, as shown in the block diagram of the present invention in FIG. 1, a three-way catalyst A disposed in an exhaust passage of an internal combustion engine and an exhaust gas on the upstream side of the three-way catalyst. An upstream air-fuel ratio sensor B which is disposed in the passage and generates an output signal according to the exhaust air-fuel ratio, and a downstream air which is disposed in the downstream exhaust passage of the three-way catalyst A and generates an output signal according to the exhaust air-fuel ratio. Based on the history of changes in the output signals of the fuel ratio sensor C, the upstream air-fuel ratio sensor B in the past predetermined period, and the current output signal of the downstream air-fuel ratio sensor C, the downstream after a predetermined time has elapsed from the present time. Estimating means D for estimating a future value of the output signal of the side air-fuel ratio sensor C, and the upstream side air-fuel ratio sensor B based on the estimated output signal of the downstream side air-fuel ratio sensor C.
Of the internal combustion engine, and a control means F for controlling the combustion air-fuel ratio of the internal combustion engine based on the corrected output of the upstream side air-fuel ratio sensor B. A device is provided.

[0011]

The exhaust air-fuel ratio on the downstream side of the three-way catalyst A has a certain delay time since the exhaust air-fuel ratio on the upstream side of the three-way catalyst A changes due to the O ₂ storage function of the three-way catalyst. Later a similar change begins. Therefore, the current three-way catalyst A
By knowing the change state of the exhaust air-fuel ratio on the upstream side, it is possible to predict the change of the exhaust air-fuel ratio on the downstream side of the three-way catalyst A after the delay time has elapsed.

The estimating means D of the present invention detects the change state of the exhaust air-fuel ratio on the upstream side of the three-way catalyst A from the change history of the output signal of the upstream side air-fuel ratio sensor B in the past predetermined period, and detects the change state. Based on the current output signal of the downstream side air-fuel ratio sensor C (that is, the current three-way catalyst downstream side exhaust air-fuel ratio), the downstream side air-fuel ratio sensor at the time when the time corresponding to the delay time has elapsed from the present time The output signal of C (exhaust air-fuel ratio) is estimated.

The correcting means E determines the output of the upstream side air-fuel ratio sensor B based on not the present output signal of the downstream side air-fuel ratio sensor C but the future output signal of the downstream side air-fuel ratio sensor C estimated as described above. to correct. Since the control means F controls the engine combustion air-fuel ratio based on the corrected output signal of the upstream side air-fuel ratio sensor B, there is a time delay when the air-fuel ratio is corrected by the output signal of the downstream side air-fuel ratio sensor C. Does not happen.

[0014]

FIG. 2 is an overall schematic view showing an embodiment of an internal combustion engine to which the air-fuel ratio control device according to the present invention is applied. In FIG. 2, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The air flow meter 3 is a device for directly measuring the intake air amount. For example, a movable vane type air flow meter having a built-in potentiometer is used, and an output signal of an analog voltage proportional to the intake air amount is generated. This output signal is input to the A / D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has its axis converted into, for example, a crank angle, a crank angle sensor 5 that generates a reference position detecting pulse signal every 720 °, and a crank angle of 30 °.
A crank angle sensor 6 that generates a pulse signal for detecting each crank is provided for each. The pulse signals of the crank angle sensors 5 and 6 are supplied to the input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder. The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 generates an electric signal of analog voltage according to the temperature of the cooling water. This output is also supplied to the A / D converter 101.

In the exhaust system downstream of the exhaust manifold 11, a catalytic converter 12 containing a three-way catalyst for simultaneously purifying three harmful components HC, CO and NOx in the exhaust gas.
Is provided. A first air-fuel ratio sensor (upstream air-fuel ratio sensor) 13 is provided in the exhaust manifold 11, that is, upstream of the catalytic converter 12, and a second air-fuel ratio is provided in the exhaust pipe 14 downstream of the catalytic converter 12. A sensor (downstream air-fuel ratio sensor) 15 is provided.

In the present embodiment, the upstream side air-fuel ratio sensor 13 generates an output signal which corresponds to the oxygen component concentration in the exhaust gas in a wide air-fuel ratio range, that is, in one-to-one correspondence with the exhaust air-fuel ratio. A full range air-fuel ratio sensor (A / F sensor) is used. There are several types of A / F sensors. FIG. 6 schematically shows the structure of a general A / F sensor. The A / F sensor 210 has a platinum electrode 21.
A solid electrolyte 213 such as zirconia is arranged between the first and the second 212, and a diffusion-controlling layer 214 made of a ceramic coating layer that restricts oxygen molecules in the exhaust gas from reaching the cathode is disposed on the surface of the cathode (exhaust-side electrode) 212. It has a structure provided. In the A / F sensor of FIG. 6, the cathode 212 is placed in contact with the exhaust gas, the anode 211 is placed in contact with the atmosphere, and both electrodes 21 are placed at a certain temperature or higher.
When a voltage is applied between Nos. 1 and 212, oxygen molecules in the exhaust gas are ionized on the cathode 212 side, and the ionized oxygen molecules move in the solid electrolyte 213 toward the anode 211 and become oxygen molecules again at the anode 211. It produces a pumping action. Due to this oxygen pumping action, a current flows between the electrodes 211 and 212 in proportion to the amount of oxygen molecules moved per unit time. However, since the diffusion rate controlling layer 214 restricts the oxygen molecules from reaching the cathode, the output current is saturated at a certain constant value, and the current does not increase even if the voltage is increased. The value of this saturation current is approximately proportional to the oxygen concentration in the exhaust gas. Therefore, by appropriately setting the applied voltage, it is possible to obtain an output current approximately proportional to the oxygen concentration. In this embodiment, this output current is converted into a voltage signal and supplied to the A / D converter 101 of the control circuit 10. Since the oxygen concentration in the exhaust and the air-fuel ratio have a one-to-one correlation, the output voltage has a one-to-one correlation with the exhaust air-fuel ratio, and the exhaust air-fuel ratio can be known from the output current. FIG. 7 shows the output characteristics of the A / F sensor 13 used in this embodiment.

On the other hand, in this embodiment, the downstream air-fuel ratio sensor 1
As 5, a so-called O ₂ sensor is used, which outputs a voltage signal according to the oxygen concentration in the exhaust gas as with the A / F sensor, but the output voltage changes relatively rapidly around the theoretical air-fuel ratio. . The O ₂ sensor has substantially the same structure as the A / F sensor shown in FIG. 6, but the diffusion rate controlling layer 214 of FIG. 6 is not provided, and the O ₂ sensor is used with the electrodes 211 and 212 opened. When the solid electrolyte 213 is exposed to the exhaust gas and the temperature rises in this state, the atmosphere side (high oxygen concentration side) electrode 211 moves to the exhaust side (low oxygen concentration side) electrode 212, contrary to the case of the A / F sensor. Since oxygen ions are moved toward the electrodes, a voltage corresponding to the difference in oxygen concentration between the atmosphere side and the exhaust side is generated between the electrodes 211 and 212. Also,
Since the oxygen concentration in the exhaust gas abruptly changes between the rich side and the lean side with the stoichiometric air-fuel ratio as a boundary, the output of the O ₂ sensor changes relatively abruptly near the stoichiometric air-fuel ratio as shown in FIG. The Z characteristic is shown.

In this embodiment, the control of correcting the output of the upstream side air-fuel ratio sensor using the output of the downstream side air-fuel ratio sensor is performed, and the downstream side air-fuel ratio sensor is related to the problem of the time delay. Since it is desirable that the response speed of the A / F sensor be as fast as possible, the downstream side air-fuel ratio sensor 15 should be an O ₂ sensor that has less aging change of the reference output voltage (theoretical air-fuel ratio equivalent output voltage) than the A / F sensor and has good response. Is used as. In the following description, the upstream air-fuel ratio sensor is the A / F sensor 13, and the downstream air-fuel ratio sensor is the O ₂ sensor 1.
We will call them 5 and distinguish them.

In this embodiment, the control circuit 10 is configured as, for example, a microcomputer, and the A / D converter 1 is used.
A RAM 104, a ROM 105, a clock generation circuit 107, and the like are provided outside the 01, the input / output interface 102, and the CPU 103. In this embodiment, the control circuit 1
0 performs basic control such as fuel injection control and ignition timing control of the engine 1, and also functions as an estimation unit, a correction unit, and a control unit described in claim 1 as described later, and controls the air-fuel ratio of the engine 1. To do.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for generating a signal indicating whether or not the throttle valve 16 is fully closed, that is, an LL signal. The idle state output signal LL is supplied to the input / output interface 102 of the control circuit 10. 1
Reference numeral 8 denotes a secondary air introduction intake valve, which supplies secondary air from an air source such as an air pump (not shown) to the exhaust pipe 11 during deceleration or idling to reduce HC and CO emissions.

Furthermore, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 are for controlling the fuel injection valve 7.
That is, in the routine described later, when the fuel injection amount (injection time) fi is calculated, the injection time fi is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, down counter 1
08 counts a clock signal (not shown), and when the output terminal finally becomes "1" level, the flip-flop 109 is set and the drive circuit 110 stops the energization of the fuel injection valve 7. . That is, the above fuel injection time fi
Only then, the fuel injection valve 7 is energized, and an amount of fuel corresponding to the time fi is sent to the combustion chamber of the engine body 1.

Incidentally, the interrupt generation of the CPU 103 is A /
For example, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6 after the A / D conversion of the D converter 101 is completed. The intake air amount data and the cooling water temperature data of the air flow meter 3 are fetched by an A / D conversion routine executed at a predetermined time or at a predetermined crank angle and stored in a predetermined area of the RAM 105. That is,
The intake air amount data and the cooling water temperature data in the RAM 105 are updated every predetermined time. Further, the rotation speed data is calculated by interruption of the crank angle sensor 6 for each 30 ° CA (crank angle) and stored in a predetermined area of the RAM 105.

As described above, in the embodiment according to the present invention, the control circuit 10 as the estimating means of claim 1 predicts the future value of the output of the downstream O ₂ sensor 15. Hereinafter, a method of predicting the output signal of the downstream O ₂ sensor 15 by the control circuit 10 will be described with reference to FIG. FIG. 3 shows the temporal change of the output voltage V _O2 of the downstream O ₂ sensor 15 when the exhaust air-fuel ratio A / F on the upstream side of the catalytic converter changes stepwise from the lean air-fuel ratio to the rich air-fuel ratio near the stoichiometric air-fuel ratio. FIG. In FIG. 3, the A / F is maintained at the rich air-fuel ratio until the time indicated by, and at the time, the rich air-fuel ratio suddenly changes to the lean air-fuel ratio. In this case, the downstream side O
The output voltage V _O2 of the ₂ sensor 15 is kept at the rich side output (about 0.9 volt) until the time ′, which is a delay time d from the above time, is reached due to the O ₂ storage action of the three-way catalyst. After that, as the oxygen stored in the three-way catalyst is exhausted, it changes to a lean output (about 0.1 volt).

The output V _O2 of the downstream O ₂ sensor 15 at the time immediately after the change remains a rich output even though the upstream side exhaust air-fuel ratio A / F changes to the lean side. The output corresponding to the upstream side exhaust air-fuel ratio A / F is obtained at time ', which is the time d elapsed from the time. Thus, the downstream O ₂ sensor for detecting the upstream-side air-fuel ratio A / F at time downstream O ₂ sensor 15 is not the downstream O ₂ sensor 15 outputs a time, a future time by the time d ' Since the output of 15 must be used, the upstream air-fuel ratio A / F at time cannot be known from the output of the downstream O ₂ sensor 15 at time.

However, the change in the air-fuel ratio on the downstream side of the catalytic converter (that is, the change in the output V _O2 of the downstream side O ₂ sensor 15) from the time to ′ is the period from the time to the time d traced back from the time by the time d. Since it corresponds to the change in the upstream side air-fuel ratio A / F during the period (-), the history of change in the upstream side air-fuel ratio A / F during the period (-) is used to estimate the air-fuel ratio downstream of the catalytic converter in ′. It is possible to

In this embodiment, as shown in FIG.
_{2 In} consideration of the response characteristics approximate to the first-order lag system of the output of the sensor 15, the period from the time d of the upstream side air-fuel ratio (output signal of the upstream side A / F sensor 13) to the present time and variation history, guess downstream O ₂ sensor 15 output value at the time that has elapsed since the current by time d in the following manner by using the current downstream O ₂ sensor 15 output value.

First, the output of the downstream O ₂ sensor 15 is approximated by a first-order lag system having a delay time d, and the downstream O ₂ sensor output V _{O2 (K)} at time _K and the immediately preceding time (K-
Downstream O ₂ sensor output V _{O2 (K-1) in 1)} and upstream A / F sensor 13 output V at time (Kd)
The relationship with _{A / F (Kd)} is expressed by the following model formula. V _{O2 (K)} = α · V _{O2 (K-1)} + β · V _{A / F (Kd)} (1) where α and β are three-way catalyst type and downstream O ₂ sensor It is a constant determined by the output characteristics, sampling interval (time interval between time K-1 and K), etc.
It is calculated in advance from the relationship. (Note that α and β may not be constants and may be set so as to change according to the output of the downstream O ₂ sensor 15.) Next, using the relationship of the equation (1), the time is calculated by the following procedure. from the downstream O ₂ sensor output V _{O2 (K)} in K, guess downstream O ₂ sensor output V _{O2 (K + d)} in the time after the time d has elapsed (K + d).

<< V _{O2 (K + 1)} >> = α * _{VO2 (K)} + β * _{VA / F (K-d + 1)} (21) _{<< VO2 (K + 2)} >> = α * V _{O2 (K + 1)} >> + β ・ V _{A / F (K-d + 2)} … (22) 《V _{O2 (K + 3)} 》 ＝ α ・ 《V _{O2 (K + 2)} 》 ＋ β ・ V _{A / F (K-d + 3)} … (23) ………………………………………………………………………………………………………… ………………… 《V _{O2 (K + d)} 》 ＝ α ・ 《V _{O2 (K + d-1)} 》 ＋ β ・ V _{A / F (K)} … (2d)

Here, _<< V _{O2 (i)} >> (that is, << V
_{O2 (K + 1)} >>, _{<< VO2 (K + 2)} >>, ..., _{<< VO2 (K + d)} >>)
Represents the estimated value of the downstream O ₂ sensor output at each time, which is obtained by using the relationship of the equation (1). Also V
_{A / F (i)} (that is, V _{A / F (K-d + 1)} , V _{A / F (K-d + 2)} , ...,
V _{A / F (K)} ) is the actual measured value of the upstream A / F sensor output.

In this way, after a lapse of time d from the history (measured value) of the output change of the upstream A / F sensor 13 in the past predetermined period d and the current output (measured value) of the downstream O ₂ sensor 15. It becomes possible to highly accurately estimate the output of the downstream O ₂ sensor. Next, the estimated value << V obtained above
The correction of the output of the upstream A / F sensor 13 based on _{O2 (K + d)} >> will be described. As will be described later, in this embodiment, the engine combustion air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio based on the output of the upstream side A / F sensor 13. For this reason,
When the output of the upstream A / F sensor 13 does not accurately reflect the exhaust air-fuel ratio due to a change in output characteristics due to deterioration of the upstream A / F sensor 13 or non-uniform mixing of exhaust gas The air-fuel ratio control deviates from the stoichiometric air-fuel ratio, which deteriorates drivability and makes it impossible to maintain the exhaust gas purification action of the three-way catalyst.

In this embodiment, the estimated value _<< V _{O2 (K + d)} >>
And the theoretical air-fuel ratio equivalent output V _O2 S of the downstream side O ₂ sensor 15, that is, assuming that there is no O ₂ storage action, the downstream side of the catalytic converter when the current upstream side exhaust gas passes through the catalytic converter. Based on the deviation of the exhaust air-fuel ratio from the stoichiometric air-fuel ratio at the current upstream side A / F sensor 1
3 Output V _{A / F (K)} is corrected. That is, the upstream side A is controlled so that the air-fuel ratio control is performed in the direction in which the deviation between the exhaust air-fuel ratio and the stoichiometric air-fuel ratio on the downstream side of the catalytic converter becomes zero.
The output of the / F sensor 13 is corrected. As a result, even if the output characteristic of the upstream A / F sensor 13 changes, the output of the upstream A / F sensor is immediately corrected and the engine combustion air-fuel ratio is always kept at the theoretical air-fuel ratio. .

In this embodiment, the following correction value ΔV
_{A / F (K)} is calculated and the current output V of the upstream A / F sensor 13
Performing output correction of the upstream A / F sensor 13 by adding the correction value [Delta] V A _{/ F (K)} to the _{A / F (K).}

ΔV_{A / F (K)}= G₁・ Δ << V_{O2 (K + d)}>> + G₂・ (_{i = 0}Σ^KΔV_{O2 (i)}+_{i = K + 1}Σ^{K + d}Δ << V_{O2 (i)}>>) + G₃・ (Δ << V_{O2 (K + d)}>>-Δ << V_{O2 (K + d-1)}>>) …… (3) and * V_{A / F (K)}= V_{A / F (K)}+ ΔV_{A / F (K)} (4) where * V_{A / F (K)}Is the upstream side A after correction at time K
/ F sensor output, Δ << V_{O2 (i)}>> (i = K + 1, K +
2, K + 3, ..., K + d) is an estimated value << V _{O2 (i)}"When
Downstream O₂Output voltage V equivalent to theoretical air-fuel ratio of sensor_O2With S
Represents the deviation. That is, Δ << V_{O2 (i)}>>
(<< V_{O2 (i)}>>-V_O2S).

Further, _{i = 0} Σ ^K ΔV _{O2 (i)} is the downstream O ₂
The sensor output measured value V _O2 and V _O2 S and deviation [Delta] V _O2 of the sum from time zero (the time of engine startup) to the current time K (integral _{value), i = K + 1 Σ} K + d Δ "V O2 _(i) "likewise estimate" K from time K + 1 for V _O2 "" deviation Δ of "V _O2
It represents the total sum (integral value) up to + d. Also, (Δ << V
_{O2 (K + d)} >>-[Delta] _< VO2 _{(K + d-1)} >>) represents the rate of change of the deviation (estimated value) at time K + d. That is, according to the above, the correction amount ΔV _{A / F (K)} is determined by the PID (proportional, integral, PID) based on the deviation between the downstream O ₂ sensor output and the stoichiometric air-fuel ratio equivalent value.
Differentiation) processing. Where G ₁ , G ₂ , G
₃ is a feedback gain constant, which is determined by experiments and the like.

FIG. 4 is a flow chart showing a routine executed by the control circuit 10 for calculating an estimated value of the downstream O ₂ sensor output 15 and correcting the output of the upstream A / F sensor 13 based on the estimated value. This routine is executed every constant rotation angle of the crankshaft (for example, every 180 ° rotation). When the routine starts in FIG. 4, step 401
Then, the outputs V _{A / F} and V _O2 are respectively A / D converted and read from the upstream A / F sensor 13 and the downstream O ₂ sensor 15. Next, at step 403, the output V _{A / F} ,
With V _O2 V _{A / F,} the current value of _{V O2 V A / F (K} ), V O2 (K)
Will be updated.

Next, at step 405, using the above current values V _{A / F (K)} and V _{O2 (K)} , the above equations (21) to (2 ₎ are used.
The estimated values _{<< VO2 (K + 1)} >> to _{<< VO2 (K + d)} >> are calculated from _d) , and in step 407 the measured value _{VO2 (K)} and the estimated value _{<< VO2 (K)
O2 (K + 1)} >> to _{<< VO2 (K + d)} >> theoretical air-fuel ratio equivalent output _VO2
Deviation from S, ΔV _{O2 (K)} , Δ << V _{O2 (K + 1)} >>
Δ _{<< VO2 (K + d)} >> is calculated.

Further, the sum of the time zero deviation [Delta] V _O2 based on the measured values of step 409 in V _O2 (when starting the engine) to the current time K (integral ^{_{value), i = 0 Σ K ΔV}} O2 (i) is operational Stored in the RAM as a variable SUM, and in step 410, time K + 1 to time K based on the estimated value of V _O2.
+ Deviation _{Δ "V O2 (K + 1} )" to d ～Deruta sum of _{"V O2 (K + d)} " ( integral _{value), i = K + 1 Σ} K + d Δ "V O2 (i)" is It is calculated and stored in the RAM as a variable << SUM >>.

Then, in step 411, the above (3)
The correction amount ΔV _{A / F (K)} is calculated from the equation, and in step 413, the corrected upstream A / F sensor output, * V _{A / F (K)} is calculated from the above equation (4). Further, step 415
Then, from V _{A / F (K-d + 1)} to V in preparation for the next routine execution
_{The value of A / F (K-1)} is updated, and then the routine ends.
In this routine, d is the number of times the routine is executed corresponding to the delay time, and is set to, for example, d = 2 to 4. That is, in this routine, the output of the downstream O ₂ sensor 15 after one or two rotations of the crankshaft is always predicted to predict the upstream A / F.
The output of the sensor 13 is corrected.

Next, the upstream A / F corrected as described above
The air-fuel ratio control based on the output * V _{A / F} of the sensor 13 will be described. There are various methods of controlling the air-fuel ratio based on the output signal of the upstream side A / F sensor, but here, in order to make the most of the O ₂ storage action of the three-way catalyst, adsorption ( An example of an air-fuel ratio control method based on modern control that allows the engine combustion air-fuel ratio to converge to the stoichiometric air-fuel ratio with high accuracy and in a short time while keeping the stored amount of oxygen at a predetermined amount. I will explain. The applicant of the present application has already proposed this air-fuel ratio control method in Japanese Patent Application No. 5-68391.

In this air-fuel ratio control method, the amount of air taken into the cylinder per engine revolution (the amount of air in the cylinder) mc is determined from the output of the air flow meter 3 and the engine speed.
And the corrected output * V of the upstream A / F sensor 13
_The combustion air-fuel ratio α is obtained from the _{A / F,} and the fuel amount fc actually supplied into the cylinder is calculated from these as fc = mc / α. Similarly, the target fuel amount fc required to make the combustion air-fuel ratio the stoichiometric air-fuel ratio by using the theoretical air-fuel ratio αr.
r is calculated as fcr = mc / αr, and the difference fc between them is calculated.
The fuel injection amount fi is determined so that −fcr and the time integrated value x1 thereof become zero at the same time.

Further, since a part of the fuel injected from the fuel injection valve 7 adheres to the wall surface of the intake port, the injection amount from the fuel injection valve 7 and the fuel amount supplied to the cylinder do not necessarily match. The fuel adhesion is taken into consideration when determining the fuel injection amount fi. As described above, the target value f
By controlling the fuel injection amount fi so that the deviation of the actual fuel supply amount from cr and the time integrated value thereof become zero at the same time, the three-way catalyst always stores a predetermined oxygen amount, and The responsiveness of air-fuel ratio control can be improved.

FIG. 5 shows a flow chart for calculating the fuel injection amount (time) fi by the above air-fuel ratio control method. This routine is executed by the control circuit 10 at every constant crank rotation angle (for example, every 360 ° rotation). If the routine is star in FIG. 5, in step 501, as shown in FIG.
The air-fuel ratio α is calculated from the output characteristic of FIG. 7 by using the output * V _{A / F} of the upstream side A / F sensor 13 corrected by the routine of FIG. Next, at steps 502 and 503, from the air-fuel ratio α obtained above, the intake air amount mc per engine revolution obtained from the output of the air flow meter 3 and the engine speed, and the theoretical air-fuel ratio αr (constant), The fuel amount fc supplied to the cylinder and the target fuel amount fcr are calculated. In step 504, the above fc and f
The deviation δfc from cr is calculated as δfc = fc−fcr.

In step 505, the nominal value fim of the fuel injection amount fi is fim _(k) = {fcr _(k) -(1-P) fwm _(k) } /
Calculated as (1-R). In the present embodiment, the fuel injection amount fi, the fuel amount fw adhering to the wall surface of the intake port of the injected fuel, and the fuel amount fc supplied to the cylinders are the nominal values fim, fwm, fcm and the deviation δfi, respectively. δfw,
It is expressed as the sum of δfc as follows.

Fi = fim + δfi fw = fwm + δfw fc = fcm + δfc It is also assumed that the following model formula is established between them. fw _{(k + 1)} = Pfw _(k) + Rfi _(k) fc _(k) = (1-P) fw _(k) + (1-R) fi _(k) fwm _{(k + 1)} = Pfwm _(k) + Rfim _(k) fcm _(k) = (1-P) fwm _(k) + (1-R) fim
_(k) fcm _(k) = fcr _(k) where the subscript k is the value at the time of execution of this routine, (k-
1) indicates the value at the time of executing the previous routine. Further, in this embodiment, P and R are constants. By modifying the above model equation, in step 505 the nominal value fim is obtained in the above form.

Next, at step 506, the time integral value x1 of δfc is set to x1 _(k) = x1 _(k-1) + δfc _(k) , and at step 507, the time integral value x2 of x1 is further changed to x2 _{(k )} = X2 _(k-1) + x1 _(k) . Further, in step 508, the deviation δfi is calculated using the values of fi, δfc, x1, x2, etc. obtained up to the previous time.
, Δfi _(k) = f1 · δfi _(k-1) + f2 · δfc _(k-1) + f3 · x1 _(k) + f4 · x1 _(k-1) + f5 · x1 _(k-2) + f6 · x2 _{(k -1)} Calculated as + f7 · x2 _(k-2) . Here, f1 to f7 are constants.

In step 509, the fuel injection amount fi is determined as fi _(k) = fim _(k) + δfi _(k) using the nominal value fim of the fuel injection amount and the deviation δfi obtained as described above.
Is required as. Further, in step 510, in preparation for the next routine execution, the nominal value of the amount of fuel adhering to the wall surface is calculated as fwm = Pfwm _(k) + Rfim _(k) using the values of fwm and Rfim at the time of execution of this routine. In steps 511 to 516, δfi _(k-1) , δfc _(k-1) , x are prepared for the next routine execution.
The values of 1 _(k-1) , x1 _(k-2) , x2 _(k-1) , and x2 _(k-2) are updated using the values at the time of execution of this routine.

From the above, the fuel injection amount (injection time) fi
Is determined, a down-counter 108 of the control circuit 10 is executed by a fuel injection routine (not shown) executed separately.
Is set to the time fi, and the drive circuit 110 injects fuel from the fuel injection valve 7 in an amount corresponding to fi. According to the above-described routine, the fuel injection amount is controlled based on the output of the upstream A / F sensor 13 corrected using the future predicted value of the output of the downstream O ₂ sensor 15.
The deviation of the air-fuel ratio from the theoretical air-fuel ratio is corrected very quickly,
High precision control is always performed.

[0049]

According to the present invention, a predetermined time has elapsed from the present using the change history of the output signal of the upstream side air-fuel ratio sensor in the past predetermined period and the present output signal of the downstream side air-fuel ratio sensor. The output signal of the downstream side air-fuel ratio sensor is estimated at this time, and the upstream side air-fuel ratio sensor output is corrected based on this estimated value, so that the response of the air-fuel ratio control due to the time delay of the downstream side air-fuel ratio sensor output As a result, it is possible to prevent deterioration of performance and perform air-fuel ratio control with high accuracy and good responsiveness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is an overall view of an internal combustion engine to which an embodiment of the present invention is applied.

FIG. 3 is a diagram for explaining a method of estimating a future value of an output of a downstream O ₂ sensor.

FIG. 4 is a flowchart of a routine for estimating output of a downstream O ₂ sensor and correcting output of an upstream A / F sensor.

FIG. 5 is a flowchart of an air-fuel ratio feedback control routine based on the output of the upstream A / F sensor.

FIG. 6 is a diagram for explaining a general structure of an A / F sensor.

FIG. 7 is a diagram showing an example of output characteristics of an upstream A / F sensor.

FIG. 8 is a diagram showing an example of output characteristics of a downstream O ₂ sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine main body 2 ... Intake passage 3 ... Air flow meter 7 ... Fuel injection valve 10 ... Control circuit 12 ... Catalytic converter 13 ... Upstream air-fuel ratio sensor 15 ... Downstream air-fuel ratio sensor

Claims (1)

[Claims] 1. A three-way catalyst arranged in an exhaust passage of an internal combustion engine, and an upstream air-fuel ratio sensor arranged in an upstream exhaust passage of the three-way catalyst for generating an output signal according to an exhaust air-fuel ratio,
A downstream side air-fuel ratio sensor which is arranged in a downstream side exhaust passage of the three-way catalyst and generates an output signal according to an exhaust air-fuel ratio, a change history of a past predetermined period of an output signal of the upstream side air-fuel ratio sensor, and the downstream side Based on the current output signal of the side air-fuel ratio sensor, an estimating means for estimating a future value of the output signal of the downstream side air-fuel ratio sensor after a predetermined time has elapsed from the present, and the estimated downstream side air-fuel ratio sensor Correcting means for correcting the current output of the upstream side air-fuel ratio sensor based on the output signal, and control means for controlling the combustion air-fuel ratio of the internal combustion engine based on the corrected output of the upstream side air-fuel ratio sensor. An internal-combustion engine air-fuel ratio control device equipped with.